Irrigated pasture productivity and its variability in the Shepparton region of northern Victoria

Abstract

The seasonal distribution and variability of growth of three types of irrigated pastures were measured at Kyabram over a period of up to seven years. The pasture types studied were (1) paspalum (Paspalum dilatatum)-dominant perennial pasture, (2) ryegrass (Lolium perenne)/clover (Trifolium repens) perennial pasture, and (3) annual pasture based on subterranean clover (Trifolium subterraneum) and Wimmera ryegrass (Lolium rigidum). The influence of environmental factors on the year-to-year variability in monthly growth rates was also examined. Annual growth curves were constructed for each pasture type, and examination of the variability about each monthly mean indicated that the spring months, and October in particular, were the most variable months for pasture growth. Environmental factors were found to account for part of the year-to-year variation in pasture growth of paspalum pastures in August, September, October, November and April. Higher mean maximum temperatures significantly increased growth in September, October and April, with the greatest response occurring in October; hours of sunshine was the significant factor influencing growth in August and November. Annual pasture growth also responded to changes in mean maximum temperature or hours of sunshine in September and October. The comparative mean annual production of paspalum pasture, ryegrass/clover pasture and annual pasture was 18.3, 18.3 and 11.0 t DM/ha, respectively. These levels of production represented 1.1, 1.2 and 1.6% conversion of photosynthetically active radiation during the growing period of the three pasture types, respectively. These levels of productivity and the animal production that should result, suggest that the pasture productivity on many irrigated dairy farms is either very low or the pasture that is grown is inefficiently utilized. Because animal productivity depends on pasture productivity more than any other single factor, farmers should make improvement of pasture growth their major aim while having regard for the variability in growth that can result from variations in environmental factors.